It is necessary that high-frequency devices used for communication apparatuses, satellites, and radars have high reliability. Along with the expansion of applicable products, cost reduction of these devices has also been an important factor.
Because a semiconductor element used in high-frequency devices is generally sensitive to humidity, when it is used in a high temperature and humid condition, water enters into the semiconductor element and thus a component thereof is damaged and characteristics of the semiconductor element are degraded. Accordingly, a measure for preventing entering of water is usually taken by accommodating the semiconductor element in an air-tight package. Not only a semiconductor element but also electronic components such as a resistance element and a condenser may be also accommodated therein. Hereinafter, a package that accommodates therein electronic components such as a semiconductor element, a resistance element, and a condenser is referred to as “electronic component package”.
However, ensuring airtightness of an electronic component package leads to an increase in the cost of components and manufacturing thereof and to an increase in the burden of quality management, which hinders cost reduction.
In recent years, a method of forming a protective film (a nitride film) on a surface of a high-frequency semiconductor element to improve its humidity resistance has been used. However, in this method, although an air-tight structure of a package becomes unnecessary by forming a protective film, high-frequency characteristics are degraded because the protective film is added. Accordingly, the thickness of the protective film has to be within a range where influences on the characteristics of the semiconductor element are permitted. As a result, a barrier effect good enough to resist to water adhesion caused by dew condensation cannot be expected, and thus a ventilation hole for preventing dew condensation is required in the package.
Furthermore, the electronic component package for a high-frequency device functions to block leakage of electromagnetic waves to outside and interference of electromagnetic waves from outside. Accordingly, the package needs to have an electromagnetic shielding structure with a metallic or conductive surface. The ventilation hole provided in the package has to be reduced to a size which electromagnetic waves cannot pass through (in a case of a 77-GHz millimeter-wave band, a permitted hole diameter is about 1 millimeter or less).
As a method of forming the ventilation hole, providing a through hole having a size needed for a shielding component (a lid) of the package is the easiest method; however, this hole becomes a path from which dust enters and thus the size of the hole needs to be reduced as much as possible. To obtain a hole diameter that has no problem even when dust enters through the hole and adheres to a wiring pattern within the package, the hole needs to be downsized to about 0.1 millimeter. However, because the hole making process becomes difficult, this is not an effective method.
Therefore, there is another method of providing an unbonded part in a bonding layer between a circuit board and a shielding component. Patent Literature 1 discloses a configuration in which, in a structure of bonding by a conductive adhesive, an adhesion layer is provided with an area where the conductive adhesive is not applied so as to form a ventilation hole (an unbonded part) and then ventilation is carried out. According to the invention of Patent Literature 1, by making the bonding layer thin in an order of several tens of micrometers, entering of dust can be prevented.